In the process of testing a partially completed oil well, one test routine is the taking of sidewall core samples. In this procedure, a gun (holding one or more bullets) is lowerd into the well bore and the bullets are fired at the sidewall. Penetration is achieved and a cylindrical plug from the sidewall is recovered in the bullet. The gun is subsequently retrieved from the well. The bullet is connected to the gun by means of a retrieval cable. This type apparatus involves a retrieval cable and a powder charge. The equipment must also convey an electrical firing signal through the powder. This requires that certain of the metal components be insulated from one another.
Detonation of the powder is an absolute essential if a sample is to be acquired. It is sometimes difficult to assure detonation. The present apparatus is a system whereby detonation is made more certain. This apparatus is a cartridge which uniquely joins a bullet with a core sample gun, the two being joined together by means of the cartridge which bolts to the bullet to anchor one end of the retrieval cable. Additionally, a second bolt protrudes from the cartridge and extends through and out of the gun sufficiently so that electrical wiring can be connected to it for providing a circuit connection for firing current. The gun body serves as ground for the electrical system. This bullet plus cartridge is thus assembled in the gun, this being accomplished safely at the surface. The equipment is then lowered into the borehole and after use is retrieved. An exposed wire incorporated in the present equipment particularly helps to assure proper detonation of the powder around the wire. The powder is around the wire within a housing for the cartridge. The exposed hot or firing wire is used to detonate the powder. A current surge is applied to the wire which becomes hot. The small wire is rather fragile compared to the bulk of the other equipment. The present invention contemplates the use of an improved wire mounting system which anchors one end of the hot wire with a bolt or stud and eyelet, and optionally locates an exploding cap beneath the wire. The hot wire is directed through a sleeve. The sleeve shelters the wire so that it is not handled roughly. All of this equipment is located inside of a plastic cartridge case. An electrical ground must be completed through the cartridge case; a non-welded, non-soldered system is used which comprises a protruding coil spring. The coil spring extends out of the cartridge case and grounds against the body of the gun. This comprises an expendable assembly. The cartridge case can be destroyed in use. An important advantage is retrieval of the stud bolts and retrieval cable so that they can be repackaged in a new cartridge case, charged with a new charge of powder and reused time and again. Retrieval and reuse reduces the cost of this expendable apparatus.
The present apparatus is summarized as a cartridge system to be loaded into a gun adjacent to a core sampling bullet. It incorporates studs extending from opposite ends of a sacrificial cartridge case. The cartridge case encloses a powder charge and two studs together through a retrieval cable. They assemble together in a nested arrangement for compactness. A firing wire with fasteners at both ends is also included and is in adjacent proximity to powder. The firing wire is shelter by routing it through a sleeve to anchor it at the opposite end capturing an optional exploding cap. A ground system is also included which extends through the cartridge case.